Biology-Inspired Adhesion

Biology-Inspired Adhesion

Ever wanted to scale a shear wall without worrying about losing your grip? How about meander across the ceiling? Thanks to inspiration from beetles and some hard work in the lab, equipment for such purposes may be at hand.

Accomplishing this type of gravity-defying feat requires a lightweight device with strong and repeatable adhesion that also easily detaches. Combining all four requirements into one piece of equipment has proven formidable for scientists, but beetle feet have led two Cornell researchers to a possible solution. The leaf beetle, in particular, uses the surface tension of water to adhere to surfaces. By making numerous tiny water bridges between its feet and the surface, the beetle generates an adhesive force 100 times its own weight. Yet, by using a peeling motion the beetle can quickly “unstick” its legs. Mimicking this design concept, the scientists fabricated a one-square-inch device capable of suspending 30 grams using only the power supplied by a 9V battery.

The prototype device consists of three plates. The top plate contains one thousand holes, each the size of a human hair, and the bottom plate holds a water reservoir. The middle plate consists of a porous layer that pumps water in a specific direction when voltage is applied. When the voltage is briefly switched on, water squeezes through each hole and forms a bridge to the target surface. The cumulative force resulting from the surface tension of the water bridges provides the adhesion. Briefly reversing the voltage pumps the water back into the reservoir, thus, breaking the bond.

According to the authors of the paper submitted to the PNAS,1 the adhesive force grows as the density of the holes grows. They estimate that the same device with one million holes (each with diameters even smaller than a human hair) could hold up more than 15 pounds. Such an apparatus covering the bottom of a standard size 12 shoe could suspend more than 500 pounds and a quick toggle of a switch would apply or release the “stickiness.” Furthermore, the whole piece of equipment would weigh a few pounds at most.

This discovery represents a growing trend of biomimicry, the utilization of designs found in nature to build devices better than previously conceived human ideas. Past advances took advantage of other beetle adhesion mechanisms, others used amoeba behavior to design better transport networks. Why do our human minds draw inspiration from other living organisms to build superior technology? And, why does our ability to draw inspiration increase as our scientific knowledge increases? I think it is difficult to answer these questions within a strictly naturalistic worldview. However, such questions find ready answers if a divine Being created all life and then fashioned humanity in His image.

  1. Michael J. Vogel and Paul H. Steen, “Capillarity-based Switchable Adhesion”, Proceedings of the National Academy of Science, preprint (February 3, 2010), doi: 10.1073/pnas.0914720107.